Most of the magazines I see in the Army now are stamped with the manufacture date (e.g. "09/00" IIRC) and "FOR GOVERNMENT / LAW ENFORCEMENT USE ONLY" or something to that effect. Most of the mags with the newer green follower have this stamp, although I don't recall if the ban and the new follower coincided at all. I'm sure someone can tell us when the new follower was introduced. I still see some mags with the older black follower, but they seem to make up about 10% of the ones in the active inventory.
Newer M9 magazines also have this type of labeling.
Most of our guys were issued their M16 mags at some point when they arrived at the unit or when they were getting ready to go to PLDC (they have to bring mags with them), so they keep them with their field gear, but as others mentioned, the magazines still belong to the Army.
Dave